Effectiveness of precision feeding in reducing N excretion in dairy cattle

Abstract

Two periods enrolling 56 (milk yield 36.2 ± 7.91 kg/d) and 58 (milk yield 32.4 ± 4.99 kg/d) grouped-fed dairy cows were performed to evaluate nutrient adjustment and N emissions of a precision feeding strategy. Pens blocked by parity were randomly assigned to a conventional (CONV) or to a precision feeding scheme (PREC) for a 21-d period. The CONV group was offered a total mixed ration (TMR, 6.82 and 6.65 MJ of NEl/kg of DM, in period 1 and 2, respectively, and 165 g of CP/kg of DM in both periods; whereas PREC cows were fed a partial mixed ration (PMR, 6.65 and 6.40 MJ of NEl/kg of DM, 135 and 137 g of CP/kg of DM, in period 1 and 2, respectively) and a concentrate feed supplemented twice daily in the milking parlour, which contained different quantities of soybean meal, corn meal, and wheat middling’s according to estimated nutritional needs of each cow above those supplied by the consumption of PMR. Individual daily nutritional needs and nutrients consumed from the PMR were calculated using a 10-d rolling average of performance data (milk yield and concentration of its components, and BW daily recorded in both periods). A N balance using urine and fecal spot sampling during the last 3 d of the study was performed in period 1, and stored manure gaseous emissions (ammonia, methane, nitrous oxide, and carbon dioxide) were measured for 2 wk in period 2. After 2 wk of adaptation to the diet, 82 cows homogeneously distributed in 4 DIM categories: early DIM (< 81), mid-early DIM (81−150), mid-late DIM (151−220), late DIM (> 220) were used to assess how energy and protein requirements were adjusted using both feeding system. Dairy cows in both feeding systems were energetically overfed, and CONV cows tended to be more CP overfed in mid-late and late DIM cows than PREC fed cows. Total daily N urine excretion, and milk N urea concentration were greater in CONV than in PREC cows. There were no differences in ammonia and nitrous oxide emissions from the manure storage between PREC and CONV cows; however, methane and carbon dioxide emissions from manure increased by 55% and 15%, respectively in PREC fed cows. Precision feeding system based on preceding average daily milk yield and composition can reduce N excretion without affecting short-term milking performance but increasing C gaseous emissions from manure.